Horton

Re: generic plans and "initial" pruning

Simon Riggs <simon.riggs@enterprisedb.com>

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From: Simon Riggs <simon.riggs@enterprisedb.com>
To: Amit Langote <amitlangote09@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2022-01-19T11:16:44Z
Lists: pgsql-hackers 
On Wed, 19 Jan 2022 at 08:31, Amit Langote <amitlangote09@gmail.com> wrote:

> > Maybe force all DDL, or just DDL that would cause safety issues, to
> > update a hierarchy version number, so queries can tell whether they
> > need to replan. Don't know, just looking for an O(1) solution.
>
> Yeah, it would be great if it would suffice to take a single lock on
> the partitioned table mentioned in the query, rather than on all
> elements of the partition tree added to the plan.  AFAICS, ways to get
> that are 1) Prevent modifying non-root partition tree elements,

Can we reuse the concept of Strong/Weak locking here?

When a DDL request is in progress (for that partitioned table), take
all required locks for safety. When a DDL request is not in progress,
take minimal locks knowing it is safe.

We can take a single PartitionTreeModificationLock, nowait to prove
that we do not need all locks. DDL would request the lock in exclusive
mode. (Other mechanisms possible).

-- 
Simon Riggs                http://www.EnterpriseDB.com/

Commits

  1. Stamp 19beta1.

  2. Revert "Don't lock partitions pruned by initial pruning"

  3. Ensure first ModifyTable rel initialized if all are pruned

  4. Fix bug in cbc127917 to handle nested Append correctly

  5. Remove unstable test suite added by 525392d57

  6. Don't lock partitions pruned by initial pruning

  7. Fix an oversight in cbc127917 to handle MERGE correctly

  8. Track unpruned relids to avoid processing pruned relations

  9. Perform runtime initial pruning outside ExecInitNode()

  10. Move PartitionPruneInfo out of plan nodes into PlannedStmt

  11. Fix setrefs.c's failure to do expression processing on prune steps.

  12. Remove obsolete executor cleanup code

  13. Revert "Move PartitionPruneInfo out of plan nodes into PlannedStmt"

  14. Move PartitioPruneInfo out of plan nodes into PlannedStmt

  15. Refactor and cleanup runtime partition prune code a little

  16. Remove some unnecessary fields from Plan trees.

  17. Remove more redundant relation locking during executor startup.

  18. Shut down Gather's children before shutting down Gather itself.